Photoconductor overcoat having a radical polymerizable charge transport molecule containing two ethyl acrylate functional groups and urethane acrylate resins containing six radical polymerizable functional groups

ABSTRACT

An improved overcoat layer for an organic photoconductor drum of an electrophotographic image forming device is provided. The overcoat layer is prepared from a curable composition including a triphenylamine charge transport containing two ethyl acrylate functional groups and a urethane resin containing six radical polymerizable functional groups. The amount of the triphenylamine charge transport containing two ethyl acrylate functional groups in the curable composition is about 20 to about 80 percent by weight. The amount of the urethane resin containing six radical polymerizable functional groups in the curable composition is about 20 to about 80 percent by weight. This overcoat layer improves wear resistance of the organic photoconductor drum without negatively altering the electrophotographic properties, thus protecting the organic photoconductor drum from damage and ultimately providing a photoconductor with a longer useful life when compared to other organic photoconductors commercially available.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.14/105,436, entitled “PHOTOCONDUCTOR OVERCOAT HAVING RADICALPOLYMERIZABLE CHARGE TRANSPORT MOLECULE CONTAINING TWO ETHYL ACRYLATEFUNCTIONAL GROUPS AND URETHANE ACRYLATE RESINS CONTAINING SIX RADICALPOLYMERIZABLE FUNCTIONAL GROUPS”, filed on Dec. 13, 2013 and assigned tothe assignee of this application.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to electrophotographic imageforming devices, and more particularly to an overcoat layer for anorganic photoconductor drum containing excellent abrasion resistance andelectrical properties.

2. Description of the Related Art

Organic photoconductor drums have generally replaced inorganicphotoconductor drums in electrophotographic image forming deviceincluding copiers, facsimiles and laser printers due to theirperformance and advantages. These advantages include improved opticalproperties such as having a wide range of light absorbing wavelengths,improved electrical properties such as having high sensitivity andstable chargeability, availability of materials, good manufacturability,low cost, and low toxicity.

While the performance and advantages offered by organic photoconductordrums are significant, inorganic photoconductor drums offer much higherdurability. Inorganic photoconductor drums (e.g., amorphous siliconphotoconductor drums) are ceramic-based, thus being extremely hard andabrasion resistant. The surface of organic photoconductor drums istypically comprised of a low molecular weight charge transport material,and an inert polymeric binder. Therefore, the failure mechanism fororganic photoconductor drums typically arises from mechanical abrasionof the surface layer due to repeated use. Abrasion of photoconductordrum surface may arise from its interaction with print media (e.g.paper), paper dust, or other components of the electrophotographic imageforming device.

The abrasion of photoconductor drum surface degrades its electricalproperties, such as sensitivity and charging properties. Electricaldegradation results in poor image quality, such as lower opticaldensity, and background fouling. When a photoconductor drum is locallyabraded, images often have black toner bands due to the inability tohold charge in the thinner regions. This black banding often marks theend of the life of the photoconductor drum.

Increasing the life of the photoconductor drum will allow thephotoconductor drum to become a permanent part of theelectrophotographic image forming device. In other words, thephotoconductor drum will no longer be a replaceable unit nor be viewedas a consumable. Photoconductor drums with a life-of-the-printer willallow the printer to operate with lower cost-per-page, more stable imagequality, and less waste.

To achieve a long life photoconductor drum, especially with organicphotoconductor drum, a protective overcoat layer may be coated onto thesurface of the photoconductor drum. An overcoat layer formed from acrosslinkable silicon material has been known to improve life of thephotoconductor drums used for color printers. However, such overcoatlayer does not have the robustness for edge wear of photoconductor drumsused in mono printers. Robust overcoat layer that improves wearresistance and extends life of photoconductor drums for both mono andcolor printers, is desired.

While a robust overcoat layer improves the life of photoconductor drums,a suitable overcoat layer is required that does not significantly alterthe electrophotographic properties of the photoconductor drum. If theovercoat layer is too electrically insulating, the photoconductor drumwill not discharge and will result in a poor latent image. On the otherhand, if the overcoat layer is too electrically conducting, then theelectrostatic latent image will spread resulting in a blurred image.Thus, a protective overcoat layer that improves life of thephotoconductor drum must also allow charge migration to thephotoconductor surface for development of the latent image with toner.

SUMMARY

The present disclosure provides an overcoat layer for an organicphotoconductor drum of an electrophotographic image forming device. Theovercoat layer is prepared from a curable composition including atriphenylamine charge transport molecule containing two ethyl acrylatefunctional groups. The amount of the triphenylamine charge transportmolecule containing two ethyl acrylate functional groups in the curablecomposition is about 20 to about 80 percent by weight. The curableovercoat composition also comprises a urethane resin containing sixradical polymerizable functional groups. The amount of the urethaneresin containing six radical polymerizable functional groups in thecurable composition is about 20 to about 80 percent by weight.

This overcoat layer improves wear resistance of the organicphotoconductor drum while still allowing development of the latent imagewith toner, thus protecting the organic photoconductor drum from damageand extending its service life.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification, illustrate several aspects of the present disclosure, andtogether with the description serve to explain the principles of thepresent disclosure.

FIG. 1 is a schematic view of an electrophotographic image formingdevice.

FIG. 2 is a cross-sectional view of a photoconductor drum of theelectrophotographic image forming device.

FIG. 3 is a graph of the voltage versus 780 nm. exposure energy for twoovercoated photoconductors.

DETAILED DESCRIPTION

It is to be understood that the disclosure is not limited in itsapplication to the details of construction and the arrangement ofcomponents set forth in the following description or illustrated in thedrawings. The disclosure is capable of other embodiments and of beingpracticed or of being carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” or “having” and variations thereof hereinis meant to encompass the items listed thereafter and equivalentsthereof as well as additional items. Further, the terms “a” and “an”herein do not denote a limitation of quantity, but rather denote thepresence of one of the referenced item.

FIG. 1 illustrates a schematic representation of an exampleelectrophotographic image forming device 100. Image forming device 100includes a photoconductor drum 101, a charge roll 110, a developer unit120, and a cleaner unit 130. The electrophotographic printing process iswell known in the art and, therefore, is described briefly herein.During a print operation, charge roll 110 charges the surface ofphotoconductor drum 101. The charged surface of photoconductor drum 101is then selectively exposed to a laser light source 140 to form anelectrostatic latent image on photoconductor drum 101 corresponding tothe image being printed. Charged toner from developer unit 120 is pickedup by the latent image on photoconductor drum 101 creating a tonedimage.

Developer unit 120 includes a toner sump 122 having toner particlesstored therein and a developer roll 124 that supplies toner from tonersump 122 to photoconductor drum 101. Developer roll 124 is electricallycharged and electrostatically attracts the toner particles from tonersump 122. A doctor blade 126 disposed along developer roll 124 providesa substantially uniform layer of toner on developer roll 124 forsubsequent transfer to photoconductor drum 101. As developer roll 124and photoconductor drum 101 rotate, toner particles areelectrostatically transferred from developer roll 124 to the latentimage on photoconductor drum 101 forming a toned image on the surface ofphotoconductor drum 101. In one embodiment, developer roll 124 andphotoconductor drum 101 rotate in the same rotational direction suchthat their adjacent surfaces move in opposite directions to facilitatethe transfer of toner from developer roll 124 to photoconductor drum101. A toner adder roll (not shown) may also be provided to supply tonerfrom toner sump 122 to developer roll 124. Further, one or moreagitators (not shown) may be provided in toner sump 122 to distributethe toner therein and to break up any clumped toner.

The toned image is then transferred from photoconductor drum 101 toprint media 150 (e.g., paper) either directly by photoconductor drum 101or indirectly by an intermediate transfer member. A fusing unit (notshown) fuses the toner to print media 150. A cleaning blade 132 (orcleaning roll) of cleaner unit 130 removes any residual toner adheringto photoconductor drum 101 after the toner is transferred to print media150. Waste toner from cleaning blade 132 is held in a waste toner sump134 in cleaning unit 130. The cleaned surface of photoconductor drum 101is then ready to be charged again and exposed to laser light source 140to continue the printing cycle.

The components of image forming device 100 are replaceable as desired.For example, in one embodiment, developer unit 120 is housed in areplaceable unit with photoconductor drum 101, cleaner unit 130 and themain toner supply of image forming device 100. In another embodiment,developer unit 120 is provided with photoconductor drum 101 and cleanerunit 130 in a first replaceable unit while the main toner supply ofimage forming device 100 is housed in a second replaceable unit. Inanother embodiment, developer unit 120 is provided with the main tonersupply of image forming device 100 in a first replaceable unit andphotoconductor drum 101 and cleaner unit 130 are provided in a secondreplaceable unit. Further, any other combination of replaceable unitsmay be used as desired. In some example embodiment, the photoconductordrum 101 may not be replaced and is a permanent component of the imageforming device 100.

FIG. 2 illustrates an example photoconductor drum 101 in more detail. Inthis example embodiment, the photoconductor drum 101 is an organicphotoconductor drum and includes a support element 210, a chargegeneration layer 220 disposed over the support element 210, a chargetransport layer 230 disposed over the charge generation layer 220, and aprotective overcoat layer 240 formed as an outermost layer of thephotoconductor drum 101. Additional layers may be included between thesupport element 210, the charge generation layer 220 and the chargetransport layer 230, including adhesive and/or coating layers.

The support element 210 as illustrated in FIG. 2 is generallycylindrical. However the support element 210 may assume other shapes ormay be formed into a belt. In one example embodiment, the supportelement 210 may be formed from a conductive material, such as aluminum,iron, copper, gold, silver, etc. as well as alloys thereof. The surfacesof the support element 210 may be treated, such as by anodizing and/orsealing. In some example embodiment, the support element 210 may beformed from a polymeric material and coated with a conductive coating.

The charge generation layer 220 is designed for the photogeneration ofcharge carriers. The charge generation layer 220 may include a binderand a charge generation compound. The charge generation compound may beunderstood as any compound that may generate a charge carrier inresponse to light. In one example embodiment, the charge generationcompound may comprise a pigment being dispersed evenly in one or moretypes of binders.

The charge transport layer 230 is designed to transport the generatedcharges. The charge transport layer 230 may include a binder and acharge transport compound. The charge transport compound may beunderstood as any compound that may contribute to surface chargeretention in the dark and to charge transport under light exposure. Inone example embodiment, the charge transport compounds may includeorganic materials capable of accepting and transporting charges.

In an example embodiment, the charge generation layer 220 and the chargetransport layer 230 are configured to combine in a single layer. In suchconfiguration, the charge generation compound and charge transportcompound are mixed in a single layer.

The overcoat layer 240 is designed to protect the photoconductor drum101 from wear and abrasion without altering the electrophotographicproperties, thus extending the service life of the photoconductor drum101. The overcoat layer 240 has a thickness of about 0.1 μm to about 10μm. Specifically, the overcoat layer 240 has a thickness of about 1 μmto about 6 μm, and more specifically a thickness of about 3 μm to about5 μm. The thickness of the overcoat layer 240 is kept at a range thatwill not provide adverse effect to the electrophotographic properties ofthe photoconductor drum 101.

In an example embodiment, the overcoat layer 240 includes athree-dimensional crosslinked structure formed from a curablecomposition. The curable composition includes a triphenylamine chargetransport molecule containing two ethyl acrylate functional groups. Inone example embodiment, the curable composition includes about 20 toabout 80 percent by weight of the triphenylamine charge transportmolecule containing two ethyl acrylate functional groups, and about 20to about 80 percent by weight of urethane resin containing six radicalpolymerizable functional groups. In more particular, the curablecomposition includes about 40 to about 60 percent by weight of the atriphenylamine charge transport molecule containing two ethyl acrylatefunctional groups and about 40 to about 60 percent by weight of theurethane resin containing six radical polymerizable functional groups.Loading the triphenylamine charge transport molecule containing twoethyl acrylate functional groups at less than 20% by weight in thecurable composition, may not provide the overcoat layer 240 withsufficient conductivity to give sufficient electrical properties forexcellent image quality. Additionally, loading the triphenylamine chargetransport molecule containing two ethyl acrylate functional groups atgreater than 80% by weight in the curable composition may not providesufficient crosslink density to give the overcoat layer 240 withsufficient abrasion resistance.

The excellent properties exhibited by the overcoat of the presentinvention are dependent upon both the choice of urethane acrylate andcrosslinkable charge transport molecule. Surprisingly, the inventorshave discovered that overcoats containing a triphenylamine chargetransport molecule containing two ethyl acrylate functional groups showsignificantly higher abrasion resistance when compared to the analogoustriphenylamine charge transport molecule containing two propyl acrylatefunctional groups. The latter crosslinkable charge transport moleculewas disclosed in U.S. Patent Application Ser. No. 13/731,594 entitled“PHOTOCONDUCTOR OVERCOATS COMPRISING RADICAL POLYMERIZABLE CHARGETRANSPORT MOLECULES AND HEXA FUNCTIONAL URETHANE ACRYLATES”.

While not wishing to be bound by theory, the inventors believe that theabrasion resistance imparted by a triphenylamine charge transportmolecule containing two ethyl acrylate functional groups results fromhigher crosslink density versus triphenylamine charge transportmolecules containing two propyl acrylate functional groups. Theethylacrylate groups of the present invention remove twonon-crosslinkable methylene fragments from the crosslinked layer,thereby increasing the crosslink density when compared to the analogouspropyl acrylate groups.

The triphenylamine charge transport molecule containing two ethylacrylate functional groups of the present invention has the generalstructure shown below:

where R is H or an alkyl group.

Limiting the value of R to a hydrogen or alkyl group provides a chargetransport molecule possessing the electrical properties sufficient totransport charge for a photoreceptor of the present invention. Inprinciple, the alkyl group may be any branched or unbranched saturatedhydrocarbon group having the general formula C_(n)H_(2n+1), wherein nis, for example, a number from 1 to about 100 or more, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tort-butyl, octyl, decyl,tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. If R is analkyl group, R contains 1 through about 12 carbon atoms, and morespecifically, 1 through about 6 carbons. Both of the ethyl acrylategroups of the present invention are in the para position of the phenylrings, relative to the nitrogen atom. The inventors have found that thispositioning gives a charge transport molecule possessing the electricalproperties sufficient to transport charge for a photoconductor of thepresent invention.

The overcoat formulation of the present invention also includes aurethane resin having six radical polymerizable functional groups. Thesix radical polymerizable functional groups of the urethane resin may bethe same or different, and may be selected from the group consisting ofacrylate group, methacrylate group, styrenic group, allylic group,vinylic group, glycidyl ether group, epoxy group, or combinationsthereof. The urethane resin containing six radical polymerizablefunctional groups may be an aromatic urethane resin, an aliphatic resin,or combinations thereof.

In an example embodiment, the aromatic urethane resin containing sixradical polymerizable functional groups is an aromatic urethane resincontaining six acrylate groups of the following structure:

and is commercially available from Sartomer Corporation under the tradename CN975.

In an example embodiment, the aliphatic urethane resin containing sixradical polymerizable functional groups is an aliphatic urethane resincontaining six acrylate groups of the following structure:

and is commercially available from Cytec Industries under the trade nameEBECRYL 8301.

Urethane acrylates containing six acrylate groups may also besynthesized using readily available starting materials, and wellestablished synthetic methods. An Example of the synthesis of CN975 isshown below.

The urethane acrylate synthesis involves reaction of a diisocyanate withpentaerythritol triacrylate. In general, urethane acrylate chemistryinvolves reaction of an isocyanate with a hydroxy acrylate in thepresence of a catalyst. In a general sense, the choice of isocyanateand/or hydroxy acrylate plays a large role in determining the mechanicaland thermal properties of the radically cured material. Curing ofurethane acrylates, such as those described above, creates a3-dimensionally crosslinked structure. Increasing the crosslink densityof the radically cured material is one way to improve the mechanical andthermal properties of the materials. Urethane resins containing sixacrylate groups are preferred since crosslink density increases with thenumber of radical polymerizable functional groups. High crosslinkdensity is known to improve properties such as abrasion and chemicalresistance. The crosslinked 3-dimensional network should be homogeneousthroughout the cured material, since this improves mechanical andthermal properties. Homogeneous crosslinking is also important forapplications requiring a high degree of optical transparency.

The combination of a triphenylamine charge transport molecule containingtwo ethyl acrylate functional groups and a urethane resin containing sixacrylate groups provides the overcoat layer 240 with excellent abrasionresistance. Urethane acrylate resins are most often used when a clear,thin, abrasion or impact resistant coating is required to protect anunderlying structure. Consequently, urethane acrylates are most commonlydeposited as thin films. Industrial applications include automotive andfloor coatings with thicknesses ranging from tens to hundreds ofmicrons. These applications, however, do not require charge migration tooccur. In an electrophotographic printer, such as a laser printer, anelectrostatic image is created by illuminating a portion of thephotoconductor surface in an image-wise manner. The wavelength of lightused for this illumination is most typically matched to the absorptionmax of a charge generation material, such as titanylphthalocyanine.Absorption of light results in creation of an electron-hole pair. Underthe influence of a strong electrical field, the electron and hole(radical cation) dissociate and migrate in a field-directed manner.Photoconductors operating in a negative charging manner moves holes tothe surface and electrons to ground. The holes discharge thephotoconductor surface, thus leading to creation of the latent image.The urethane resins containing six acrylate groups of the presentinvention lack charge transporting properties, thus limiting thethickness of the overcoat layer 240. The addition of a triphenylaminecharge transport molecule containing two ethyl acrylate functionalgroups in the curable composition provides the overcoat layer 240 withelectrical properties that approach those of the underlying chargetransport layer 230. The presence of a triphenylamine charge transportmolecule containing two ethyl acrylate functional groups in the overcoatlayer 240 allows the thickness of the overcoat layer to be increasedwithout having significant adverse effects on the electrical propertiesof the photoconductor drum 101. Ultimately this overcoat formulation ofthe present invention leads to a photoconductor drum having an ‘ultralong life’, thereby allowing a consumer to successfully print at least100,000 pages on their printer before they have to go purchase areplacement photoconductor drum.

The present invention describes a photoconductor overcoat layercontaining the unique combination of a triphenylamine charge transportmolecule containing two ethyl acrylate functional groups and a urethaneresin containing six acrylate groups. This combination provides both theabrasion resistance of the urethane acrylate and the charge transportingproperties of the radical polymerizable charge transport molecule.Additionally, the overcoat of the present invention has (1) excellentadhesion to the photoconductor surface, (2) optical transparency and (3)crack free. Overcoat delamination (poor adhesion) from thephotoconductor surface has been noted as a problem in the prior art.Overcoat layers are typically coated in solvent systems designed tosolubilize components of the overcoat formulation, while minimizingdissolution of the underlying photoconductor structure. Dissolution ofcomponents comprising the underlying photoconductor results in materialswith no radical polymerizable functionality entering the overcoat layer.The result is dramatically lower crosslinking density and lower abrasionresistance since the properties of the overcoat layer are optimized byan uninterrupted 3-dimensional network. Ideally, the overcoat layer isdistinct from the underlying photoconductor surface. However, theinterface between the overcoat and the photoconductor surface oftenlacks the chemical interactions required for strong adhesion. Theovercoat of the present invention have excellent adhesion to thephotoconductor surface throughout the print life of the photoconductor.The overcoat must also be optically transparent. Illumination of thephotoconductor in an image-wise manner requires that layers not involvedin the charge generation process be transparent to the incident light.Additionally, optical transparency is an indicator of material andcrosslink homogeneity within the overcoat structure. The overcoat of thepresent invention has a high degree of optical transparency throughoutthe print life of the photoconductor. The overcoat must also be crackfree. UV or Ebeam cured films often exhibit cracks as a result ofunrelieved internal stress. These cracks will manifest immediately inprint, and will dramatically decrease the functional life of theovercoat. The overcoats of the present invention are crack freethroughout the print life of the photoconductor.

The curable composition may further include a monomer or oligomercontaining at most five radical polymerizable functional groups. The atmost five radical polymerizable functional groups of the monomer oroligomer may be selected from the group consisting of acrylate group,methacrylate group, styrenic group, allylic group, vinylic group,glycidyl ether group, epoxy group, or combinations thereof.

Suitable examples of mono-functional monomers or oligomers include, butare not limited to, methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,isobornyl acrylate, isobornyl methacrylate, 2-phenoxyethyl acrylate, andlauryl methacrylate.

Suitable examples of di-functional monomers or oligomers include, butare not limited to, diacrylates and dimethacrylates, comprising1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, ethyleneglycol dimethacrylate, diethylene glycol diacrylate, diethylene glycoldimethacrylate, triethylene glycol diacrylate, triethylene glycoldimethacrylate, 1,3-butylene glycol diacrylate, 1,6-hexanedioldiacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanediolmethacrylate, tripropylene glycol diacrylate, 1,3-butylene glycoldimethacrylate, 1,3-butylene glycol dimethacrylate, cyclohexanedimethanol diacrylate esters, or cyclohexane dimethanol dimethacrylateesters.

Suitable examples of tri-functional monomers or oligomers include, butare not limited to, trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate, hydroxypropyl acrylate-modified trimethylolpropanetriacrylate, ethylene oxide-modified trimethylolpropane triacrylate,propylene oxide-modified trimethylolpropane triacrylate, andcaprolactone-modified trimethylolpropane triacrylate. More specifically,the tri-functional monomer or oligomer includes propoxylated (3)trimethylolpropane triacrylate, ethoxylated (6) trimethylolpropanetriacrylate, propoxylated (6) trimethylolpropane triacrylate, andethoxylated (9) trimethylolpropane triacrylate.

Suitable examples of monomers or oligomers containing four radicalpolymerizable functional groups include, but are not limited to,pentaerythritol tetraacrylate, di-trimethylolpropane tetraacrylate, andethoxylated pentaerythritol tetraacrylate.

Suitable examples of monomers or oligomers containing five radicalpolymerizable functional groups include, but are not limited to,pentaacrylate esters and dipentaerythritol pentaacrylate esters.

The curable composition may further include a non-radical polymerizableadditive such as a surfactant at an amount equal to or less than about10 percent by weight of the curable composition. More specifically, theamount of non-radical polymerizable additive is about 0.1 to about 5percent by weight of the curable composition. The non-radicalpolymerizable additive may improve coating uniformity of the curablecomposition.

The curable composition is prepared by mixing the urethane resin andcharge transport molecules in a solvent. The solvent may include organicsolvent such as tetrahydrofuran (THF), toluene, alkanes such as hexane,butanone, cyclohexanone and alcohols. The solvent may include a mixtureof two or more organic solvents to solubilize triphenylamine chargetransport molecule containing two ethyl acrylate functional groups andthe urethane resin containing six radical polymerizable functionalgroups.

The curable composition may be coated on the outermost surface of thephotoconductor drum 101 through dipping or spraying. If the curablecomposition is applied through dip coating, an alcohol is used as thesolvent to minimize dissolution of the components of the chargetransport layer 230. The alcohol solvent includes isopropanol, methanol,ethanol, butanol, or combinations thereof.

The coated curable composition is then exposed a radiation source ofsufficient energy to induce formation of free radicals to initiate thecrosslinking. The exposed composition is then post-baked to anneal andrelieve stresses in the coating. The radiation source of sufficientenergy to induce formation of free radicals is either a UV source, or anebeam source. If a UV source is used to generate free radicals, thecurable composition may contain a photoinitiator.

Specific examples of photo initiators for use under UV cure conditionsinclude acetone or ketal photo polymerization initiators such asdiethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one,1-hydroxy-cyclohexyl-phenyl-ketone,4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone,2-benzyl-2-dimethylamino-1-(4-molpholinophenyl)butanone-1,2-hydroxy-2-methyl-1-phenylpropane-1-oneand 1-phenyl-1,2-propanedion-2-(o-ethoxycarbonyl)oxime; benzoinetherphoto polymerization initiators such as benzoin, benzoinmethylether,benzoinethylether, benzoinisobutylether and benzoinisopropylether;benzophenone photo polymerization initiators such as benzophenone,4-hydroxybenzophenone, o-benzoylmethylbenzoate, 2-benzoylnaphthalene,4-benzoylviphenyl, 4-benzoylphenylether, acrylated benzophenone and1,4-benzoylbenzene; thioxanthone photo polymerization initiators such as2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone,2,4-diethylthioxanthone and 2,4-dichlorothioxanthone; phenylglyoxylatephotoinitiators such as methylbenzoylformate and other photopolymerization initiators such as ethylanthraquinone,2,4,6-trimethylbenzoyldiphenylphosphineoxide,2,4,6-trimethylbenzoyldiphenylethoxyphosphineoxide,bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide,bis(2,4-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphineoxide,methylphenylglyoxyester, 9,10-phenanthrene, acridine compounds, triazinecompounds and imidazole compounds. Further, a material having a photopolymerizing effect can be used alone or in combination with theabove-mentioned photo polymerization initiators. Specific examples ofthe materials include triethanolamine, methyldiethanol amine,4-dimethylaminoethylbenzoate, 4-dimethylaminoisoamylbenzoate,ethyl(2-dimethylamino)benzoate and 4,4-dimethylaminobenzophenone. Thesepolymerization initiators can be used alone or in combination. Theloading of photoinitiator is between about 0.5 to about 20 parts byweight and more specifically from about 2 to about 10 parts by weightper 100 parts by weight of the curable composition.

Curing the composition by ebeam does not require the presence of aphotoinitiator and thus may result in greater crosslink density. In anexample embodiment, the radiation source of sufficient energy to induceformation of free radicals is ebeam.

Preparation of Example Photoconductor Drum

A photoconductor drum was formed using an aluminum substrate, a chargegeneration layer coated onto the aluminum substrate, and a chargetransport layer coated on top of the charge generation layer.

The charge generation layer was prepared from a dispersion includingtype IV titanyl phthalocyanine, polyvinylbutyral,poly(methyl-phenyl)siloxane and polyhydroxystyrene at a weight ratio of45:27.5:24.75:2.75 in a mixture of 2-butanone and cyclohexanonesolvents. The polyvinylbutyral is available under the trade name BX-1 bySekisui Chemical Co., Ltd. The charge generation dispersion was coatedonto the aluminum substrate through dip coating and dried at 100° C. for15 minutes to form the charge generation layer having a thickness ofless than 1 μm, specifically a thickness of about 0.2 to about 0.3 μm.

The charge transport layer was prepared from a formulation includingterphenyl diamine derivatives and polycarbonate at a weight ratio of50:50 in a mixed solvent of THF and 1,4-dioxane. The charge transportformulation was coated on top of the charge generation layer and curedat 120° C. for 1 hour to form the charge transport layer having athickness of about 17 μm to about 19 μm as measured by an eddy currenttester.

EXAMPLE 1

The inventive overcoat layer including two ethyl acrylate functionalgroups was prepared from a formulation including4,4′-di(acrylyloxyethyl)-4″-methyl-triphenylamine (20 g), EBECRYL 8301(20 g) and ethanol (80 g). The formulation was coated through dipcoating on the outer surface of the Example Photoconductor Drumdescribed hereinabove.

The inventive coated layer was then exposed to an ebeam source at anaccelerating voltage of 90 kV, a current of 3 mA, and an exposure timeof 1.2 seconds. The ebeam cured photoreceptor was then thermally curedat 120° C. for 60 minutes. The cured layer forms the overcoat layerhaving a thickness of about 3.8 μm as measured by an eddy currenttester.

COMPARATIVE EXAMPLE 1

An overcoat layer was prepared from a formulation including4,4′-di(acrylyloxypropyl)triphenylamine (20 g), EBECRYL 8301 (20 g) andethanol (80 g). The formulation was coated through dip coating on theouter surface of the Example Photoconductor Drum described above. Thecoated layer was then exposed to an ebeam source at an acceleratingvoltage of 90 kV, a current of 3 mA, and an exposure time of 1.2seconds. The ebeam cured photoreceptor was then thermally cured at 120°C. for 60 minutes. The cured layer forms the overcoat layer having athickness of about 3.9 μm as measured by an eddy current tester.

The photoconductor drums prepared in Example 1 and Comparative Example 1were evaluated on an in-house electrostatic tester. The test results areshown in FIG. 3. The graph describes the photoconductor surface voltageas a function of 780 nm. laser exposure energy. The graph in FIG. 3shows that the electrical properties derived from the inventive overcoathaving 4,4′-di(acrylyloxyethyl)-4″-methyl-triphenylamine are nearlyidentical to the prior art overcoat having4,4′-di(acrylyloxypropyl)triphenylamine). This shows that thephotoconductor drum overcoated with 2 ethyl acrylate functional groupsmaintain good electrical properties. These results show that theimproved abrasion resistance imparted by the crosslinkable chargetransport molecule of the present invention, and described in Table 1,do not come at the expense of a degradation in electrical properties.

Photoconductor drums from Example 1 and Comparative Example 1 wereinstalled in an electrophotographic image forming device. Theelectrophotographic image forming device was then operated at 50 ppm ina four-page and pause run mode. Eddy current measurements were recordedevery 20 k prints. The test was stopped when the average thickness lossexceeded the initial overcoat thickness. The initial thickness of theovercoat, print count, and the initial and end of test image printquality are summarized in Table 1.

TABLE 1 Overcoat Print Image Quality Image Photoconductor ThicknessCount (Beginning Quality Drum (μm) (k Prints) of Test) (End of Test)Example 1 4.4 140 Excellent Excellent Comparative 4.5 100 ExcellentExcellent Example 1

As illustrated in Table 1, the photoconductor drum having the inventiveovercoat containing 4,4′-di(acrylyloxyethyl)-4″-methyl-triphenylamine(Example 1) was run for an additional 40k prints when compared to anidentically prepared drum having an overcoat containing4,4′-di(acrylyloxypropyl)triphenylamine (Comparative Example 1). Thisresult is very favorable when trying to produce photoconductor drum withan ultra long life. Moreover, in addition to having a longer life, thephotoconductor drum having the inventive overcoat maintained excellentprint quality, darkness and image resolution and showed much lesselectrical fatigue when compared to a non-overcoated drum. The inventorsbelieve that lower electrical fatigue results from the high abrasionresistance, and thus less thickness loss, imparted by the drumsovercoated with the inventive formulation.

The foregoing description illustrates various aspects of the presentdisclosure. It is not intended to be exhaustive. Rather, it is chosen toillustrate the principles of the present disclosure and its practicalapplication to enable one of ordinary skill in the art to utilize thepresent disclosure, including its various modifications that naturallyfollow. All modifications and variations are contemplated within thescope of the present disclosure as determined by the appended claims.Relatively apparent modifications include combining one or more featuresof various embodiments with features of other embodiments.

What is claimed is:
 1. A method of preparing a photoconductorcomprising: providing an electrically conductive substrate; preparing acharge generation layer dispersion; coating the charge generation layerdispersion onto the electrically conductive substrate to form a chargegeneration layer; preparing a charge transport layer dispersion; coatingthe charge transport layer dispersion over the charge generation layerto form a charge transport layer ; preparing a protective overcoat layerformulation, the protective overcoat layer being formed from a curablecomposition including: about 20 to about 80 percent by weight of atriphenylamine charge transport molecule containing two ethyl acrylatefunctional groups as shown below:

wherein R is selected from the group consisting of H and an alkyl group;and about 20 to about 80 percent by weight of a urethane acrylate resincontaining six radical polymerizable functional groups, an organicsolvent and a photoinitiator, coating the protective overcoat layerformulation over the charge transport layer; and curing the protectiveovercoat layer formulation to form a photoconductor having a protectiveovercoat layer over the charge transport layer and the charge generationlayers.
 2. The method of claim 1, wherein the curable compositionincludes: about 40 to about 60 percent by weight of a triphenylaminecharge transport molecule containing two ethyl acrylate functionalgroups; and about 40 to about 60 percent by weight of a urethaneacrylate resin containing six radical polymerizable functional groups.3. The method of claim 1, wherein R is a hydrogen atom.
 4. The method ofclaim 1, wherein R is an alkyl group containing 1 to about 6 carbonatoms.
 5. The method of claim 1, wherein the urethane resin of theurethane resin containing six radical polymerizable functional groups isan aliphatic urethane resin.
 6. The method of claim 1, furthercomprising the step of adding a non-radical polymerizable additive tothe curable composition.
 7. The method of claim 1, wherein theprotective overcoat layer has a thickness of about 0.1 μm to about 10 μmupon curing.